Severe sepsis and septic shock are life-threatening problems frequently encountered in the critical care unit. Current treatments based on antibiotic therapy, inotropes, fluid resuscitation, and end-organ support are not always effective, and there is an urgent need for new therapies to reduce sepsis mortality. One ongoing effort is to remove or inactivate circulating endotoxins (or lipopolysaccharides, LPS), which are primarily responsible for the pathophysiological derangements seen in gram-negative sepsis. Several compounds that can bind to lipid A, an anionic glycolipid serving as a toxic element of LPS, via antigen-antibody interactions, electrostatic interactions, or hydrophobic interactions have been explored for the treatment of sepsis. However, these therapies have made little clinical impacts. The difficulties partly arise from their hydrophobicity and cationic charge, the very properties used for interaction with LPS, as they cause toxicity and non-specific interactions with proteins and other blood components. We propose to develop a new therapeutic agent for systemic sepsis treatment based on our chitosan derivative, which we call zwitterionic chitosan (ZWC). ZWC is created by partial amidation of low molecular weight chitosan (CS) but distinct from CS by the charge profile and water solubility. Unlike CS, ZWC is negatively charged and water-soluble at physiological pH and thus compatible with blood components. Importantly, it suppresses the production of pro-inflammatory cytokines by LPS-challenged macrophages via extracellular interaction with LPS. Moreover, IP-administered ZWC mitigated systemic effect of LPS or attenuated the onset of LPS-induced sepsis in mice, with no signs of adverse tissue responses seen with CS. These features well justify the investigation of ZWC as a novel LPS antagonist. Our long-term goal is to develop a new systemic treatment for sepsis based on ZWC. The objective of this study is to produce a ZWC, comparable or superior to polymyxin B in efficacy and potency but with no systemic toxicities, and to investigate the utility of ZWC as a systemic therapy of sepsis. Our central hypothesis is that ZWC suppresses LPS activity via direct interaction with LPS and binding to receptors of LPS/TLR4 signaling pathways; therefore, ZWC modifications to increase these properties will improve the potency and efficacy of ZWC. To test this hypothesis, we will modify ZWC with additional hydroxyl groups and hydrophobic pendants and evaluate its in vitro anti-LPS activity of optimized ZWC benchmarking it against polymyxin B (Aim 1) and in vivo therapeutic effects of the optimized ZWC in a mouse model of severe sepsis as a standalone therapy as well as a supplement to standard care procedure (Aim 2). The proposed work is expected to optimize the properties of ZWC for best therapeutic outcomes and prove the effectiveness of ZWC in systemic treatments of sepsis. Successful accomplishment of this study will provide a new way to neutralize LPS and reduce the sepsis-related mortality, complementing the current standard of care of sepsis.